Wave guide attenuator



Nov. 24, 1953 w. ALTAR 2,660,713

WAVE GUIDE ATTENUATOR Filed May 15, 1948 Basis an ce Ma zera'al [1? 501a 1:219 Ma ferz'a Z WITNESSES: INVENTOR William Hlzar.

ATTORNEY I Patented Nov. 24, 1953 UNITED STAT-E3 ft? NT OF FICE; I

14 i Claims. 1

My invention relates to the conduction of electromagnetic energy and it has particular relation to attenuators for such energy.

Attenuators in accordance with the teachings of the prior art of which I am aware include a highresistance disposed in a wave guide. Where the energyfiowingthrough the guide is substantial, the-attenuators of this type tend to become h'otand their characteristics change. To avoid thisunde'sirable condition, the attenuators are maintained at constant temperature by a system of-water cooling. Such apparatus necessarily is 'costly' and cumbersome. The cooling system often leaks andoperation'of the apparatus must bediscontinued until the leaks are found and repaired;

It is; accordingly; an;:object of my invention to provide apparatus for the-attenuation of an oscillating electric field. which has constant re sistance;

Another object of my invention, is to provide apparatus for the attenuation ofan'oscillating electric field which is simple to manufacture.

Stillanother object of myinvention'is to provide'method and'apparatus for the attenuation of-anoscillating-electric field which-is dependable.

In-accordance with my invention; I provide apparatus in which the attenuation-is effected by=-arotating discwhichextends into awave guide-a controllable-distance. The disc is coated with--a-resistance material on one or both'sides near theedge. Poweris supplied tothe disc'to produce-the'rotation' so that one part is cooling while another is-being'heated-by the oscillating field in the wave guide;

The novel features that I- consider characteristic of my invention are set forth with. particularity inthe appended claims; The invention itself, however, both, as to its organization and-its method of operation, together with. addi tional objects and advantages thereof, will best be understood from the following description of specific embodiments when readin connection with theaccompanying drawing, in'which:

Figure l -is-aperspective view partly insectiorr-of-anembodiment-or my invention and Fig; 2-is an elevation view of the essential features of 'my invention.

Theapparatus shown in Fig. 1 comprises a sectionof Wave guide 4 of. rectangular cross section with an opening-6 inone of its sides, pref erablyin the middle of the side of greatest area. Extending through this opening into the interior of- -the wave guide is partiof a disc 8;'p refer ably 2. formed of an insulating material such as'fiber glass Micarta. Preferably the plane of the disc lies perpendicular to the side of greatest area. Coated on one or both sides of the disc isaresistance material I9, said resistance material need not cover the entire-face of thedisc but may cover only that portion near the edge of the disc; which extends into the waveguide. Preferably, the resistance material is aconductive substance havinga; resistance substantially greater than that of the inner surface ofthe guide. A suitable material for this coating" is a colloidal suspension of carbon known as aquadag which may be coated on the disctoa thickness of the order of two or'three thou-'- sandths of an inch to provide a resistance-preferably of the order of1200ohms per-square;

The term ohmspersquare is commonly used in designating the resistance of a layer, coating or sheet of material to an edgewise currentsuch as would be found in ultra-high frequency 'work where currents flow 'edgewise in a very-thin layer at the surface ofa conductive material upon which electromagnetic "Waves are incident. As is well known in this field, the ohmsper square resistance ofa layer of material is equal to the resistivity; constant of the materialdivided'by the thickness of the layer.

Since the plane of the disc 8' is perpendicular to the side of greatest-area of theguide 4', it is substantially parallel to the electric-field- I2 of the electromagnetic-wave conducted through the guide. With the surface of the disc parallel-=to the electric field, currents flow in the conductive layer on the disc and the resistance of the-layer efiects an appreciable loss in energy. The quantity of energy so absorbed for-a layer of 'a given resistance-persquare depends on the area of the layer in the field and the strength of the field at the position of'the layer.

In my apparatus the disc is mounted soas to enable the adjustment of thedistance which it extends into the oscillating field in the wave guide. I am, therefore, able to adjust the area of the layer in the field and thus adjust the quantity of energy absorbed.

The mounting shown in the drawing for th-is adjustmentcomprisesa metal bar l4 hinged'to'a stationary support iii-'resting-on the waveguide at one end, a screw it attachedto the bar near its center and extending to another support/-28 fastened to the wave guide, the screw beingyso attached that rotating variesthe distance between the bar and the wave guide. Fastened to the bar Hi near the opposite end of the, bar. from that which is fastened to the stationary support [6, is the disc 8. The disc is mounted on an axle 22 which, in turn, is connected to a small motor 24 so that the disc rotates constantly. The disc may also be turned by constructing it with fins 26 so that it would turn when in the presence of an air current. An electric fan, or similar device could then be used to supply this air current.

The oscillating electric field in the wave guide, on coming in contact with the resistance surface of the disc will lose part of its energy to that section of the disc which is in the wave guide. The energy absorbed by the resistance surface of the disc will appear in that section of the disc in the form of heat. As the wheel is constantly turning, that section oi the disc which is in the wave guide being heated is constantly changing.

As a section passes out of the wave guide, it cools in the air to approximately its original temperature before returning to the interior of the wave guide. Thus the variations in temperature are suppressed since each section leaves the region inside the wave guide before being appreciably changed in temperature. The cooling efiect can be made more efficient by employing a fan to blow air against the disc or by placing fins 26 on the disc so as to direct a current of air against the resistance surface as the disc rotates.

While I have shown and described certain specific embodiments of my invention, it is obvious that many other variations thereof may be employed without departing from the spirit of the invention. For this reason I do not intend to limit my invention to the specific embodiments disclosed.

I claim as my invention:

1. Wave guide attenuator comprising a section of wave guide with an opening in its side, a disc mounted to rotate about an axis perpendicular to said disc through its center and a mounting to support said disc in such manner that it extends into the wave guide through said opening, means capable of causing said disc to rotate, said disc being coated with a resistance material, said disc and the coating of resistance material being so shaped and so mounted that the distance which said coating extends into said wave guide remains constant during the rotation of said disc.

2. Wave guide attenuator comprising a section of wave guide with an opening in its side, and a disc mounted to rotate about an axis perpendicular to said disc through its center, a mounting to support said disc in such manner that said disc extends into the wave guide through said opening, a coating of resistance material on said disc, said disc being so constructed as to rotate when an air current strikes it, and a source of said air current.

3. Wave guide attenuator comprising a section of wave guide with an opening in its side, and a disc mounted to rotate about an axis perpendicular to said disc through its center, said disc mounting being arranged to support said disc in such manner that it extends into the wave guide through said opening, coating on said disc of resistance material, a motor connected to said disc in such manner as to cause it to rotate, and means cooperative with said motor and said mounting means for varying at the will of an operator the distance which said disc extends into said wave guide.

4. Wave guide attenuator comprising a section of wave guide with an opening in its side, and a disc mounted to rotate about an axis perpendicular to said disc through its center, means capable of causing said disc to rotate continuously during operation, said disc mounting being arranged to support said disc in such manner that it extends into the wave guide through said opening, a coating of resistance material on said disc, and means cooperative with said mounting and said rotating means for varying at the will of an operator the area of surface of the disc lying inside said wave guide,

5. A wave guide attenuator comprising a section of wave guide, an opening in a side of said wave guide, a disc mounted to rotate about an axis perpendicular to said disc through its center, a mounting to support said disc in such manner that it extends into said wave guide through said opening, said disc being coated with a resistance material said disc, the coating of resistance material and said mounting being so designed that said disc is capable of being rotated without substantially varying the distance which said coating extends into said wave guide.

6. An attenuator arrangement for wave guides, comprising, a disc of wave attenuation material, means to support said disc so that an adjustable portion of its area extends through a slot in a wall of the guide, means to maintain said disc in continuous rotation, and means to subject the external portion of said disc to a cooiing air blast.

'1. An attenuator arrangement for hollow wave guides, comprising, means defining a slot through one wall of the guide, a pivotally mounted arm, an attenuator disc, means to support said disc for rotation on said arm and with a portion of said disc extending through said slot into the wave guide, motor means for maintaining said disc in continuous rotation, means to adjust said arm and thereby to adjust the attenuating effect of said disc in said guide, and means to direct a blast of cooling air on the said disc external to said guide.

8. In combination, a hollow wave guide of the rectangular type having means to propagate wave energy thcrethrough in a transverse electric mode, a rotatably mounted disc of insulating material having a carbonized surface, said disc extending through a slot in the wave guide wall so that the plane of the disc is parallel to the direction of wave propagation, means to adjustably support said disc to control the effective area thereof extending in said direction of propagation and thereby to control the amount of attenuation, means to maintain said disc in continuous rotation at any given setting of said effective area and Without changing the extent ofsaid effective area, and means to cool the area of said disc which is exterior to said wave guide.

9. Wave guide attenuator comprising a section of wave guide with an opening in its wall, a disc incorporating an electrical resistance material mounted to rotate about an axis perpendicular to said disc through its center, a mounting to support said disc in such manner that it extends into the wave guide through said opening, said mounting including means for setting the distance which said disc extends into said guide at the will of the operator and means capable of causing said disc to rotate, said disc being so shaped and so mounted that at any setting the area of said resistance material of said disc which extends into said wave guide remains constant during the rotation of said disc.

10. Wave guide attenuator comprising a section of wave guide with an opening in its wall, a circular disc mounted to rotate about an axis perpendicular to said disc through its center, said disc incorporating a concentric closed ring of resistance material having an outer diameter approximately equal to the diameter of said disc, a mounting to support said disc in such manner that it extends into the wave guide through said opening, said mounting including means for setting the distance which said disc extends into said guide at the will of the operator and means capable of causing said disc to rotate.

11. Wave guide attenuator comprising a section of wave guide with an opening in its side, and a disc mounted to rotate about an axis perpendicular to said disc through its center, said disc mounting to support said disc in such manner that it extends into the wave guide through said opening, a motor for rotating said disc, and a coating of resistance material on said disc covering completely at least the portion of the surface of said disc which extends into said guide as the disc is rotated by said motor.

12. In combination, a section or wave guide, a disc with a resistance material on its surface, a motor mounting to support said disc in such manner that it extends into said wave guide, said disc being so connected to said motor that it rotates, and said resistance material covering substantially the whole area of said disc which extends into said Wave guide as said disc is rotated by said motor.

13. In combination, a disc with a resistance material on its surface, a motor mounting to 6 support said disc so that it extends into an oscillating electric field, said disc being so connected to said motor that said disc is caused to rotate, said resistance material extending at least over the Whole portion of the disc which projects into said field as said disc rotates.

14. Wave guide attenuator comprising a section of wave guide with an opening in its side, a disc mounted to rotate about an axis perpendicular to said disc through its center, and a mounting to support said disc in such manner that it extends into the wave guide through said opening, means capable of causing said disc to rotate, said disc incorporating a resistance material, said resistance material being so disposed on said disc and said disc being so mounted that the distance which said resistance material extends into said wave guide remains constant during the rotation of said disc.

WILLIAM ALTAR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,306,282 Samuel Dec. 22, 1942 2,505,557 Lyman Apr. 25, 1950 OTHER REFERENCES Techniques and Facilities for Microwave Radar Testing, published in A. I. E. E. Technical Paper 46-40 in January 1946, Published by A. I. E. E., 33 West 39th Street, New York, N. Y. 

